CN107061027B

CN107061027B - Active front wheel steering current control for engine start/stop vehicles

Info

Publication number: CN107061027B
Application number: CN201710037919.1A
Authority: CN
Inventors: 哈菲兹·沙菲克·卡菲兹; 阿提拉·本纳克; 柯克·佩布瑞; 格雷戈里·津巴; 埃里克·迈克尔·拉德马赫
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2016-01-19
Filing date: 2017-01-19
Publication date: 2022-06-03
Anticipated expiration: 2037-01-19
Also published as: CN107061027A; DE102017200285A1; US10407046B2; US20170203747A1

Abstract

The present disclosure relates to active front wheel steering current control for an engine start stop vehicle. A vehicle includes an engine configured to be automatically stopped and automatically started. The vehicle also includes an electric actuator for the active front wheel steering system. Before the engine is automatically stopped, control to reduce the required current of the electric actuator is started. After the engine is automatically started, control to increase the required current of the electric actuator is started.

Description

Active front wheel steering current control for engine start/stop vehicles

Technical Field

The present application relates generally to controlling an active front wheel steering system in a vehicle that includes an engine start/stop function.

Background

Micro-hybrid vehicles or start/stop vehicles may selectively shut off their engine during portions of the travel cycle to conserve fuel. As an example, a start/stop vehicle may shut off its engine when the vehicle is stopped rather than allowing the engine to idle. The engine may then be restarted, for example, when the driver depresses the accelerator pedal. The start/stop vehicle may further include an active front wheel steering system that changes a gear ratio at which wheels are steered in response to rotation of a steering wheel.

Disclosure of Invention

In some configurations, a vehicle includes an engine. The vehicle also includes an active front wheel steering system that includes an electric actuator. The vehicle further includes a controller, the controller further configured to: in response to receiving a request to shift the engine to an automatic stop state while a required current of the electric actuator exceeds a predetermined current, the required current is reduced to the predetermined current at a predetermined rate before shifting the engine to the automatic stop state to prevent an increase in engine speed (flair of the engine).

Some configurations may include one or more of the following features. In the vehicle, the controller is further configured to: the demand current is reduced at a predetermined rate in response to the vehicle decelerating to a speed less than a predetermined speed. In the vehicle, the predetermined current is a current level that prevents transition to the auto-start state. In the vehicle, the predetermined rate is such that the reduction in the required current is completed within a predetermined amount of time. In the vehicle, the predetermined amount of time decreases as the difference between the present operation current and the predetermined current decreases. In the vehicle, the controller is further configured to: the engine is shifted to an automatic stop state in response to the required current reaching a predetermined current. In the vehicle, the predetermined current is a current level that allows the engine to be shifted to the automatic stop state.

In some configurations, a vehicle includes an engine. The vehicle also includes an active front wheel steering system that includes an electric actuator. The vehicle further includes a controller configured to: in response to a demand current request of the electric actuator being greater than a predetermined threshold value during an engine autostart, the demand current of the electric actuator is increased to a level of the demand current request within a predetermined period of time after completing the autostart to prevent a drop in engine speed (sag of the engine).

Some configurations may include one or more of the following features. In the vehicle, the controller is further configured to: the demand current is increased in response to a generator connected to the engine being in an operating mode to provide electrical energy. In the vehicle, the controller is further configured to: the demand current is increased at a predetermined rate. In the vehicle, the controller is further configured to: the demand current is increased to an intermediate current that is less than the level of the demand current request at a first predetermined rate and then increased to the level of the demand current request at a second predetermined rate. In the vehicle, the first predetermined rate is greater than the second predetermined rate. In the vehicle, the controller is further configured to: in response to the demand current request becoming greater than the predetermined threshold value after completion of the automatic start, the demand current is increased to the level of the demand current request for a predetermined period of time to prevent the engine speed from dropping.

In some configurations, a method for controlling a demand current of an electric actuator of an active front wheel steering system in a vehicle, comprises: in response to an engine automatic stop request, a required current of an electric actuator is reduced by a controller at a predetermined rate based on a maximum engine torque reduction rate to prevent an engine speed from rising.

Some configurations may include one or more of the following features. The method can comprise the following steps: in response to completion of the automatic engine start, a required current of the electric actuator is increased at another predetermined rate based on a maximum engine torque increase rate by the controller to prevent a drop in engine speed. The method can comprise the following steps: the method further comprises increasing, by the controller, the demanded current at the further predetermined rate for a first predetermined time and, after the first predetermined time, increasing the demanded current at a further predetermined rate for a second predetermined time. The method can comprise the following steps: after the first predetermined time and before increasing the demanded current at the further predetermined rate, maintaining, by the controller, the demanded current at a predetermined current value for a predetermined maintenance time. In the method, the further predetermined rate is greater than the further predetermined rate. The method can comprise the following steps: the required current is reduced to a predetermined current level by the controller in response to an engine automatic stop request.

Drawings

FIG. 1 is a diagram of an exemplary start/stop vehicle showing typical components.

FIG. 2 is a diagram of an exemplary steering system including active front wheel steering.

FIG. 3 is a diagram illustrating engine states during an autostop event.

FIG. 4 is a timing diagram depicting possible current versus engine start/stop states with a single rate of increase.

FIG. 5 is a timing diagram depicting possible current versus engine start/stop conditions with two increasing phases.

FIG. 6 is a flow chart depicting a possible sequence of operations for managing active front wheel steering current demand during engine autostart and autostop events.

Detailed Description

Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely exemplary and that other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As one of ordinary skill in the art will appreciate, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combination of features shown provides a representative embodiment for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations.

FIG. 1 depicts an exemplary block diagram of a vehicle. Vehicle 110 may include an engine 112 for propelling vehicle 110. The engine 112 may be mechanically coupled to the electric machine 114. The electric machine 114 may function as an alternator and a starter. When operating as a starter, the electric machine 114 may receive power from the battery 116 via the power grid 118. The electric machine 114 may convert the electrical power into mechanical rotation to rotate the engine 112, thereby starting the engine 112.

When operating as an alternator or generator, the electric machine 114 may convert the mechanical energy generated by the rotation of the engine 112 into electrical energy on the power grid 118. The electrical energy may be stored within the battery 116 or utilized by electrical components connected to the power grid 118.

The vehicle 110 may include a steering system 128, the steering system 128 including a steering mechanism 124 connected to front wheels of the vehicle 110. The Steering system 128 may include an Active Front Steering (AFS) module 120. The AFS module 120 may assist the drive steering mechanism 124 in changing the gear ratio at which the wheels are steered in response to rotation of the steering wheel. For example, at lower vehicle speeds, a high gear ratio may be implemented such that the steering wheel rotation is less for a given steering angle. This allows a sharp turn to be accomplished with less steering wheel input. At higher vehicle speeds, the gear ratio may be reduced so that the steering wheel turns more for a given steering angle. This reduces the sensitivity of the steering system 128 to steering wheel changes at higher speeds. The net effect is: at higher speeds, the wheel rotation is less in response to a given amount of steering wheel rotation.

The steering system 128 may include an Electric Power Assist Steering (EPAS) module 122, and the electric power assist steering module 122 may cooperate with the steering mechanism 124. The EPAS module 122 may assist in driving the steering mechanism 124 to reduce the amount of effort required by the operator to steer the vehicle 110. The EPAS module 122 may include an electric motor that assists in driving the steering mechanism 124. In addition to the torque provided by the operator, the EPAS module 122 may also increase the torque to change the direction of the front wheels.

The AFS module 120 and the EPAS module 122 may be electrically connected to the power grid 118. Power may be provided to the power grid 118 by energy stored within the battery 116. When operating as a generator, the electric machine 114 may also provide electrical power to the power grid 118. The electric machine 114 is operable to maintain a predetermined voltage on the power grid 118. The torque of the motor 114 may be adjusted using voltage feedback control to maintain the predetermined voltage. For example, the magnitude of the torque of the motor 114 may be reduced in response to the voltage of the power grid 118 exceeding a predetermined voltage. The AFS module 120 and EPAS module 122 may communicate with one or more controllers 126 within the vehicle.

The vehicle 110 may include one or more controllers 126 to coordinate and manage the operation of the various components. The one or more controllers 126 may interface with various devices via hardwired signals or a serial communication bus, such as a Controller Area Network (CAN). The controller 126 may include a microprocessor and non-volatile memory for storing data when the controller 126 is powered down.

The controller 126 may be configured to automatically stop and automatically start the engine 112. During vehicle operation, the engine 112 may be stopped and started during an ignition cycle. Conditions may be monitored to determine when to automatically stop the engine 112 to improve fuel economy. Conditions may also be monitored to determine when to automatically start the engine 112.

Referring to FIG. 3, an engine start/stop sequence may include several phases: "automatic stop start", which marks the start of the automatic stop of the engine; "prepare for engine auto stop", which is the period of time for which the vehicle system and engine are prepared for an impending engine stop (if an auto stop inhibit condition is detected at this stage, preparation for the impending engine stop is interrupted, the vehicle system and engine are returned to their normal operating mode); "fuel cut", which marks the stop of fuel flow to the engine at that point; "the engine is stopping", which is a period of time during which the engine speed decreases to zero; "low fuel restart," which marks that after this point, if a restart is requested during the "engine is stopping" phase to prohibit an automatic stop, it may be necessary to engage the starter to turn (crank) the engine (if a restart is requested before the "low fuel restart" and during the "engine is stopping" phase, the automatic stop may be prohibited by restarting the engine by again turning on fuel flow); "engine speed is 0", which indicates that the engine speed at this point is close to or equal to 0; "the engine has been automatically stopped", which is a period of time when the engine is off; "Starter engaged", which marks the point at which the starter begins to turn the engine in an effort to start the engine (in response to detecting an engine autostart condition); "Starter-cranking engine", which is a period of time in which the engine cannot turn under its own power; "Starter off" which marks the point at which the engine can turn under its own power; "engine speed increase", which is a period of time during which the rotational speed of the engine increases to its operating rotational speed; "end of autostart", which marks the point at which the engine speed reaches its operating speed (equal to or higher than the target idle speed). An engine autostop event may include all phases from "autostop start" to "autostart end".

Fig. 2 depicts a diagram of an exemplary steering system 128. Steering system 128 may be configured to steer vehicle 110 in a direction desired by an operator. Steering system 128 may include a steering wheel 150 operated by an operator. Steering system 128 may translate the motion of steering wheel 150 into displacement of front wheels 152 to cause a change in direction of vehicle 110. The steering mechanism 124 may be a rack (rack)160 and pinion (pinion)162 configuration in which the front wheels 152 are coupled to the rack 160 and the steering wheel 150 is coupled to the pinion 162.

The AFS module 120 may include an electric actuator or motor 156 connected to a differential or planetary gear set 158. The motor 156 may rotate the gear 162, which may move the rack 160 and redirect the front wheel 152. The steering wheel 150 may also be connected through an AFS gear set 158. Upon turning the steering wheel 150, a variable gear ratio between the steering wheel 150 and the wheels 152 may be achieved by operating the AFS module 120 to drive the gear 162. The transmission ratio may be a ratio between a steering wheel angle and a wheel turning angle (e.g., a wheel steering angle). The AFS controller 154 may receive a steering wheel angle input signal 164 indicative of the position of the steering wheel 150 and may generate one or more output signals 166 for operating the motor 156. The AFS controller 154 may use other inputs and outputs. The AFS controller 154 may communicate with other controllers, such as an engine controller or a vehicle system controller.

The AFS controller 154 may be configured to monitor a steering wheel angle input signal 164 from the steering wheel 150. The steering ratio may be determined based on the steering wheel angle and the vehicle speed. Based on the steering ratio, the AFS controller 154 may determine a requested demand current for the motor 156. The AFS controller 154 may control the current through the motor 156 via an output signal 166.

The AFS module 120 may include a locking mechanism 168. The locking mechanism 168 may be an electromagnetic actuation device that, when actuated, prevents the motor 156 from rotating the gear 162. When the locking mechanism 168 is engaged, the AFS module is unable to assist in vehicle steering, using the output of the steering wheel 150 to effect steering. The locking mechanism 168 may be controlled by an output signal 170 from the AFS controller 154.

The EPAS module 122 and AFS module 120 are connected to the power grid 118 and obtain power from the motor 114 or battery 116. During operation, the EPAS module 122 and the AFS module 120 may draw a significant amount of current from the power grid 118. Under conditions where the engine 112 is running and the electric machine 114 is supplying power to the power grid 118, the energy stored in the battery 116 may not be consumed. However, when the engine 112 is not running, power is provided by the battery 116. The result may be a voltage drop of the power grid 118, which may negatively affect the EPAS module 122 or the AFS module 120. For example, the voltage may drop low enough that the EPAS module 122 or AFS module 120 may not function adequately.

During an engine autostop event, the voltage drop across the battery 116 may be monitored. During an engine autostop event, when the electric machine 114 is no longer providing power to the power grid 118, the voltage of the battery 116 may drop. The voltage of the battery 116 may drop to a minimum calibratable threshold. Since the AFS system 120 may draw relatively large currents, it is helpful to manage the current draw during engine autostop and autostart.

During an engine auto stop event, the EPAS module 122 may operate in a restricted mode. The EPAS module 122 may be configured to provide no assistance during an engine auto-stop event. Optionally, the EPAS may be operated to provide assistance at a reduced capacity during an engine auto stop event. During an engine auto-stop event, the EPAS module 122 may be operated such that the maximum current drawn by the EPAS module 122 is less than a predetermined threshold. The resulting vehicle effect is that during an engine autostop event, the operator torque required to steer the vehicle increases.

The operation of the AFS system 120 can be based on an operating state or condition of the engine start stop system. The operating state of the engine start stop system may be broadcast to the controller over the communication link. The engine start stop system may be operated in one or more different states or phases that may affect the operation of the AFS system 120.

The AFS controller 154 may operate the electric actuator 156 based on a request to change the steering ratio. In response to a request to change the steering ratio, the AFS controller 154 may determine the required current of the electric actuator 156. Other inputs, such as vehicle speed, may also be used to determine the required current. The AFS controller 154 may then cause an electrical current having the magnitude of the demanded current to flow through the electrical actuator 156. The mode of operation of the AFS system 120 can be based on the state of the engine start/stop system. The AFS controller 154 may receive an input indicative of an engine autostop event.

In preparation for transitioning to the engine auto stop mode, the AFS current may be reduced. During operation, the AFS 120 may draw a substantial amount of current from the power grid 118 or the battery 116. The electric machine 114 is operable to provide electric current to the AFS 120 when the engine 112 is in an operating state. When the engine 112 is in the auto-stop state, the battery 116 must provide current to the AFS 120. When the engine 112 has been automatically stopped, it may be desirable to prevent large currents from being drawn from the battery 116. Before allowing the engine 112 to automatically stop, it may be desirable to reduce the demand current of the electrical actuator 156 of the AFS 120 to a reduced current level. However, a sudden decrease in the AFS current may cause a sudden increase in the voltage output by the motor 114. In response to the increase in voltage, the voltage control strategy may decrease the torque magnitude command transmitted to the motor 114 to maintain the voltage at a predetermined level. The electric machine 114 torque change may occur faster than the engine torque change. In this case, the torque load on the engine 112 may decrease faster than the engine torque decreases, resulting in an increase in engine speed. The difference in torque response may cause an increase or rise in engine speed (flair), which makes the driver aware that the vehicle speed may increase.

To reduce engine speed rise (engine flair), the AFS current may be controlled to decrease to allow the engine control strategy to adjust engine torque to prevent changes in engine speed. For example, the AFS demand current can be reduced at a predetermined rate of reduction. In some configurations, the demand current for the electrical actuator 156 may be ramped down to a predetermined current for a predetermined amount of time. The predetermined current may be an amount of current that causes the AFS 120 to operate at a minimum performance level. The predetermined amount of time may be determined based on a response time of the engine torque reduction. For example, the rate of current reduction may be based on a maximum rate of engine torque reduction. The predetermined rate of change of reduction may correspond to a maximum rate of reduction of engine torque that the engine control system is capable of achieving.

After automatically starting the engine 112, the AFS current may be restored to the normal operating current. However, a rapid increase in AFS current may result in a decrease in the power grid voltage. Further, the electric machine 114 may respond to torque changes faster than the engine 12. In response to a decrease in the grid voltage, the motor torque may be increased, which causes the engine speed to drop resulting in the driver being aware that the vehicle speed may decrease. In this case, the torque load on the engine 112 may increase faster than the engine torque increases, resulting in a decrease in engine speed.

When the AFS 120 is restored to normal operating current, the AFS current can be controlled to prevent undesirable engine speed variations. The AFS current may be increased at a predetermined rate of increase. In some configurations, the AFS demand current may be ramped up to a normal operating current for a predetermined amount of time. The predetermined amount of time may be determined based on a response time of the engine torque increase. For example, the rate of increase may be based on a maximum rate of increase of engine torque. The predetermined rate of increase change may correspond to a maximum rate of increase of engine torque that the engine control system is capable of achieving.

FIG. 4 depicts a plot of AFS demand current versus engine start stop state. For example, when the engine 112 is in the run state, the AFS 120 can operate at a current level up to the normal operating level 404. When the normal operating level 404 is allowed, the AFS functionality can be fully supported. The normal operating level 404 may depend on the steering wheel operation and when an AFS operation is required. The AFS current reduction phase 400 may be initiated when the engine 112 is in a state ready for an engine auto stop. After the AFS current reduction phase 400, the AFS current may be limited to a limited operating level 406. The limited operation level 406 may be continued while the engine is in the auto-stop state.

After the engine is automatically started, the current ramp-up phase 402 may begin. The current increase phase 402 may be a linear ramp up of the current to a normal operating level 404 at a predetermined rate of increase.

FIG. 5 depicts a plot of selectable AFS demand current versus engine start stop state. When the engine is in the running state, the AFS 120 can operate at a current level up to the normal operating level 508. When the normal operating level 508 is allowed, the AFS functionality can be fully supported. The normal operating level 508 may depend on the steering wheel operation and when AFS operation is required. The AFS current reduction phase 500 may begin when the engine 112 is in a state ready for an engine auto stop. After the AFS current reduction phase 500, the AFS current may be limited to a limited operating level 510. The limited operation level 510 may be continued while the engine is in an auto-stop state. After the engine 112 is automatically started, a first current increase phase 502 may begin, followed by an intermediate current level 504. The first current increase phase 502 may be a linear ramp up of the AFS current up to an intermediate current level 504 at a first predetermined rate of increase. The intermediate current level 504 may be followed by a second current increase phase 506. The second current increase phase 506 may be a linear ramp up of the current to the normal operating level 508 at a second predetermined rate of increase. The first predetermined rate of increase may be different from the second predetermined rate of increase. In some configurations, the first predetermined rate of increase may be greater than the second predetermined rate of increase. This may allow the AFS current to be rapidly increased to a limited AFS support level that allows some AFS functionality.

FIG. 6 depicts a flow chart of a possible sequence of operations that may be implemented in the AFS controller 154. At operation 600, the vehicle is in an engine auto-stop state. At operation 602, it may be checked whether the engine 112 is running and the electric machine 114 is producing electrical energy (e.g., the engine and generator are running). If the engine and generator are running, operation 604 may be performed. If the engine or generator is not running, operation 602 may be repeated.

At operation 604, the AFS current may be ramped up to the requested demand current at a predetermined ramp-up rate. The increase in current may be a linear increase or a ramp up. In some configurations, the increase in current may have different rates of increase in different current increase phases. The predetermined rate of increase may be based on a maximum rate of increase of engine torque. At operation 606, a check may be made to determine the currentWhether the increase is complete. The check may be based on expiration of a predetermined amount of time or the AFS current being greater than or equal to a threshold K₁. The threshold may be a demand current of the AFS system that is dependent on a request for steering system operation. If the current increase is complete, operation 608 may be performed. If the current increase is not complete, execution may return to operation 604.

At operation 608, full AFS support may be implemented. The AFS 120 can be made to operate at currents up to the maximum AFS operating current and full AFS functionality can be achieved. At operation 610, an impending engine autostop condition may be checked. The impending engine autostop condition may include vehicle deceleration to a speed less than a predetermined speed threshold, application of a braking system, and/or status indications from a powertrain controller. If the impending engine autostop condition is not met, execution may return to operation 608. If the impending engine autostop condition is met, operation 612 may be performed.

At operation 612, the AFS current may be reduced to a minimum current value at a predetermined reduction rate. The predetermined rate of reduction may be based on a maximum rate of engine torque reduction. At operation 614, a check may be performed to determine if the current reduction is complete. The check may be based on expiration of a predetermined amount of time or the AFS current becoming less than or equal to a predetermined current limit K₂. If the AFS current reduction is not complete, execution may return to operation 612. If the AFS current reduction is complete, operation 616 may be performed. At operation 616, the engine autostop may be completed. Subsequently, the operation may return to operation 600.

The processes, methods or algorithms disclosed herein may be delivered to/implemented by a processing device, controller or computer, which may include any existing programmable or dedicated electronic control unit. Similarly, the processes, methods or algorithms may be stored as data and instructions that are executable by a controller or computer in a variety of forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information variably stored on writable storage media such as floppy disks, magnetic tapes, optical disks, RAM devices and other magnetic and optical media. The processes, methods, or algorithms may also be implemented as software executable objects. Alternatively, the processes, methods or algorithms may be implemented in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), state machines, controllers or any other hardware components or devices, or a combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously mentioned, the features of the various embodiments may be combined to form further embodiments of the invention, which may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being advantageous over other embodiments or prior art implementations in terms of one or more desired characteristics, those of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, ease of maintenance, weight, manufacturability, ease of assembly, and the like. Accordingly, embodiments described as less desirable in one or more characteristics than other embodiments or prior art implementations are not outside the scope of the present disclosure and may be desirable for particular applications.

Claims

1. A vehicle, comprising:

an engine;

an active front wheel steering system including an electric actuator;

a controller configured to: in response to receiving a request to shift the engine to an automatic stop state when a required current of the electric actuator exceeds a predetermined current, the required current is decreased to the predetermined current at a predetermined rate corresponding to a maximum engine torque decrease rate before shifting the engine to the automatic stop state.

2. The vehicle of claim 1, wherein the controller is further configured to: reducing the demanded current at the predetermined rate in response to the vehicle decelerating to a speed less than a predetermined speed.

3. The vehicle of claim 1, wherein the predetermined current is a current level that prevents transition to an autostart state.

4. The vehicle according to claim 1, wherein the predetermined rate is such that the reduction in the required current is completed within a predetermined period of time.

5. The vehicle according to claim 4, wherein the predetermined period of time decreases as a difference between a present operating current and the predetermined current decreases.

6. The vehicle of claim 1, wherein the controller is further configured to: in response to the required current reaching the predetermined current, the engine is shifted to an automatic stop state.

7. The vehicle according to claim 1, wherein the predetermined current is a current level that allows a transition of the engine to an automatic stop state.

8. A vehicle, comprising:

an engine;

an active front wheel steering system including an electric actuator;

a controller configured to: in response to a demand current of an electric actuator being limited to a predetermined level during an engine autostart, the demand current of the electric actuator is increased to a level of a demand current request at a predetermined rate of increase corresponding to a maximum rate of increase of engine torque for a predetermined period of time after the autostart is completed.

9. The vehicle of claim 8, wherein the controller is further configured to: the demand current is increased in response to a generator connected to the engine being in an operating mode to provide electrical energy.

10. The vehicle of claim 8, wherein the controller is configured to: the electric current of the electric actuator is increased to the level of the demand current request at the predetermined increase rate for a predetermined period of time.

11. A method for controlling a demand current for an electric actuator of an active front wheel steering system in a vehicle, comprising:

reducing, by a controller, a required current of an electric actuator at a predetermined rate in response to an engine automatic stop request to prevent an engine speed from rising, wherein the predetermined rate is based on a maximum engine torque reduction rate; and reducing, by the engine controller, torque of the engine at the maximum engine torque reduction rate.